A large and growing population of users is enjoying entertainment through the consumption of digital media, such as music, movies, images, electronic books, and so on. The users employ various electronic devices to consume such media. Among these electronic devices (referred to herein as “user equipment” or “UEs”) are electronic book readers, cellular telephones, personal digital assistants (PDAs), portable media players, tablet computers, netbooks, laptops, and the like. Providing a wide and increasing variety of applications and services, these electronic devices each include at least one antenna to support wireless communications with a communications infrastructure.
Mobile devices may include antennae capable of communication across multiple frequency bands. A single “multi-band” antenna may support communications on multiple frequency bands. Among other bands commonly supported by mobile devices are bands for 2.4 GHz and 5 GHz wireless local area network (WLAN) (i.e., IEEE 802.11 “WiFi” standards) communications, the 2.4 GHz band for Bluetooth communications, and various bands assigned to cellular data communications. Some services may be supported on some of the frequency bands available to a device but not on others.
In the United States, regulatory approval has been granted to a very low energy level, short-range, high-bandwidth communications technology generally referred to as “ultra-wideband.” Ultra-wideband is approved for unlicensed use across a frequency range from 3.1 to 10.6 GHz. Within this spectrum, which is also used by several other communications technologies, communications are spread over a bandwidth exceeding the lesser of 500 MHz or 20% of the arithmetic center frequency. Uses for the technology include personal area networks (PANs) and close-proximity wireless data transfers between devices, such as the direct streaming video from a personal media device to a nearby display.
Progress on the development of standards utilizing ultra-wideband has been slow. One of the obstacles to adoption of the technology has been the difficulties relating to the design of antennae that can support efficient low power operation across a substantial portion of the ultra-wideband spectrum.
In view of the limited physical space available in mobile devices such as cellular telephones and tablet computers, the need to optimize space utilization, and the general trend for devices to get smaller—rather than larger—with each generation, increasing the space dedicated to antennae necessitates design trade-offs (e.g., reducing the size of the battery) that may result in improving one feature at the expense of another.
Past solutions to expand the bandwidth have resulted in increasing the size of multi-band antennae, such as adding multiple active tuning elements to extend bandwidth, or using separate antennae to achieve cover additional frequency bands. For example, one type of mutli-band antenna used in mobile devices is a Planar Inverted F Antenna (PIFA). A PIFA resembles an inverted F, which explains the PIFA name, and can be designed to have multiple branches that resonate at different radio frequencies. However, PIFA antennae typically exhibit a degree of parasitic coupling and destructive interference between resonant modes associated with the various tuning elements, reducing the overall efficiency of the design. Moreover, while PIFA can be designed to support resonance at more than one frequency band, they are poorly suited for wideband applications that require a broad range of the radio spectrum to operate. Efficient operation across the spectrum is particularly critical for ultra-wideband applications, as such communications use low power signals proximate to the background RF noise “floor.”